Updated

Wider insurance coverage erased racial differences in who got minimally invasive surgery in Massachusetts, according to a new study.

After the state increased access to insurance in 2006, racial disparities in the proportion of people having gallbladders or appendixes removed with minimally invasive techniques - versus traditional "open" surgery - disappeared, researchers found.

"The Massachusetts experience provides a really unique and natural experiment to measure the effect of insurance expansion," Dr. Andrew Loehrer, the study's lead author from Massachusetts General Hospital in Boston, said.

Still, Loehrer also urged caution in applying these results to the nationwide expansion of insurance under the Affordable Care Act, more commonly known as Obamacare.

"Massachusetts is unique among states for many reasons in terms of healthcare delivery," he said.

Minimally invasive surgery, also called laparoscopic surgery, is the preferred way to remove gallbladders and appendixes. The technique is tied to fewer side effects, shorter recovery times and shorter hospitalizations, the researchers write in JAMA Surgery.

During laparoscopic surgery, a doctor makes small incisions into which very thin instruments and a tiny camera are inserted, and the organ is often removed through the same small opening.

Previous research has shown that minorities are less likely to receive minimally invasive surgery, compared to whites. That difference has been partially linked to gaps in insurance.

In 2006, Massachusetts reformed its healthcare system to increase the number of people with insurance. The changes included an expansion of Medicaid, the government-run health insurance program for the poor, and requiring people to purchase insurance.

Loehrer and his colleagues analyzed data on the 10,917 appendix and gallbladder removals between 2001 and 2009 to see if the state's insurance expansion had any effect on the racial gap among people receiving minimally invasive surgery.

The researchers compared their state's numbers to 156,643 appendix and gallbladder removals in six other states: New York, New Jersey, Maryland, Arizona, Florida and Washington.

Before the 2006 reforms, the probability of black and Hispanic patients receiving minimally invasive surgery in Massachusetts was about 5.2 percentage points lower than for whites. That compared to about a 1.4 percentage point difference between the same patient groups in the other states.

After the reforms, the researchers found no difference in the probability of minorities or whites receiving the less invasive procedures in Massachusetts.

In contrast, there was growing disparity within the six other states. Collectively, they saw the probability of minority patients receiving minimally invasive surgery expand to about 3.2 percentage points lower than for whites.

Loehrer said it could be that black and Hispanic patients who gained insurance during the reforms may have started going to their primary care doctors more. That would allow their conditions to be caught earlier and make them better candidates for minimally invasive surgery.

Amresh Hanchate, an assistant professor at the Boston University School of Medicine, echoed that idea: "In this study, it's much more likely that people who have symptoms will go to the doctor (after insurance expansion) sooner and will be better candidates for the minimally invasive surgery."

Hanchate, who was not involved in the new study, said the findings do not surprise him, because he published similar results on racial disparities in Massachusetts among people undergoing more major operations on other parts of the body.

"Here in Massachusetts we have a real-life experiment to answer that question and at least here it says increasing insurance coverage has a real effect on those disparities," Loehrer said.